In modern wireless devices one of the most important figures of merit is power consumption and, consequently, operation time. In order to reduce power consumption, device defines low-power states.
The power consumption of a circuit includes leakage power and switching power. Leakage power is attributed to leakage current that flows through semiconductors components (such as transistors, diodes, and the like) while switching power is attributed to switching activities of these semiconductor components.
Power gating technique involves operating a circuit (such as a processor) at a maximal frequency and a maximal supply voltage level during activation periods and shutting down the circuit during deactivation periods.
FIG. 1 illustrates a power consumption of a circuit that executes a task when a power gating technique is applied. During activation period 20 the circuit receives maximal voltage supply and clock signal of maximal frequency. Its power consumption includes leakage power consumption (box 12) and dynamic power consumption (box 14). During deactivation period 21 the circuit is shut down and does not consume any power. The sum of deactivation period 21 and activation period 20 is referred to as task period 22.
The overall power consumption of the circuit is illustrated by step-shaped curve 16 and is equal to: [DP(Vmax)+LP]*(Ta/Tt); wherein DP(Vmax) is the dynamic power consumption of the circuit when a maximal voltage (Vmax) is supplied to the circuit, LP is the leakage power consumption, Ta is the duration of activation period 20 and Tt is the duration of task period 22.
FIG. 2 illustrates a power consumption of a circuit that executes a task when a dynamic voltage and frequency scaling technique is applied. During task period 22 the circuit receives a voltage supply (Vs) that is lower than Vmax and receives clock signal of a frequency (Fc) that is lower than the maximal frequency. Its power consumption during task period 22 includes leakage power consumption (box 32) and dynamic power consumption (box 34). Task period 22 is followed by idle period 40 during which the circuit consumes leakage power 32.
The overall power consumption of the circuit is illustrated by step-shaped curve 36 and is equal to: [DP(Vs)+LP]*Tt; wherein DP(Vs) is the dynamic power consumption of the circuit when a voltage (Vs, Vs<<Vmax) is supplied to the circuit, LP is the leakage power consumption, and Tt is the duration of task period 22.
The leakage power depends on the temperature of the circuit and is hard to predict. Accordingly, selecting between these mentioned above power reduction technique is not accurate. In addition, direct measurements of the leakage current of a circuit and its switching current requires to temporarily stop the execution of circuit normal tasks and allocating time for current measurements.